Extended display identification data is stored in an internal storage element of a display device and is used to describe various parameters of the display capability of the display device. In general, the extended display identification data includes basic information and display parameters, such as manufacturer, serial number, clock and resolution of the display device. When a signal source such as a computer host or a game console is connected to the display device, the extended display identification data is first read so as to avoid the outputted display signal exceeding the display capacity of the display device. However, for various signal sources such as different hosts or different display cards, a single extended display identification data would be unable to meet the display requirements of different signal sources. Therefore, it is necessary to think about how to process the extended display identification data so that the data meet the needs of the corresponding signal source.